

A023814


Number of associative binary operations on an nset; number of labeled semigroups.


12




OFFSET

0,3


LINKS

Table of n, a(n) for n=0..9.
A. Distler and T. Kelsey, The semigroups of order 9 and their automorphism groups, arXiv preprint arXiv:1301.6023, 2013.
C. Noebauer, Home page [broken link]
C. Noebauer, The Numbers of Small Rings
C. Noebauer, Thesis on the enumeration of nearrings
Eric Postpischil Posting to sci.math newsgroup, May 21 1990
Eric Weisstein's World of Mathematics, Semigroup.
Index entries for sequences related to semigroups


CROSSREFS

Cf. A001423, A001426, A023813, A023815, A027851.
a(n)+A079172(n)=A002489(n)
Sequence in context: A072402 A092084 A099715 * A217772 A062126 A222520
Adjacent sequences: A023811 A023812 A023813 * A023815 A023816 A023817


KEYWORD

nonn


AUTHOR

Lyle Ramshaw (ramshaw(AT)pa.dec.com)


EXTENSIONS

a(8), a(9) from Distler and Kelsey (2013).  N. J. A. Sloane, Feb 19 2013


STATUS

approved



